Many plant species are capable of being transformed with transgenes to introduce agronomically desirable traits or characteristics. The resulting plant species are developed and/or modified to have particular desirable traits. Generally, desirable traits include, for example, improving nutritional value quality, increasing yield, conferring pest or disease resistance, increasing drought and stress tolerance, improving horticultural qualities (e.g., pigmentation and growth), imparting herbicide tolerance, enabling the production of industrially useful compounds and/or materials from the plant, and/or enabling the production of pharmaceuticals.
Transgenic plant species comprising multiple transgenes stacked at a single genomic locus are produced via plant transformation technologies. Plant transformation technologies result in the introduction of a transgene into a plant cell, recovery of a fertile transgenic plant that contains the stably integrated copy of the transgene in the plant genome, and subsequent transgene expression via transcription and translation of the plant genome results in transgenic plants that possess desirable traits and phenotypes. However, mechanisms that allow the production of transgenic plant species to highly express multiple transgenes engineered as a trait stack are desirable.
Likewise, mechanisms that allow the expression of a transgene within particular tissues or organs of a plant are desirable. For example, increased resistance of a plant to infection by soil-borne pathogens might be accomplished by transforming the plant genome with a pathogen-resistance gene such that pathogen-resistance protein is robustly expressed within the roots of the plant. Alternatively, it may be desirable to express a transgene in plant tissues that are in a particular growth or developmental phase such as, for example, cell division or elongation. Furthermore, it may be desirable to express a transgene in leaf and stem tissues of a plant to provide tolerance against herbicides, or resistance against above ground insects and pests.
Therefore, a need exists for new gene regulatory elements that can drive the desired levels of expression of transgenes in specific plant tissues.